1. Field of the Invention
This invention relates to a fuel injection valve for injecting fuel into an internal combustion engine, and particularly to a nozzle hole plate thereof.
2. Description of the Related Art
A fuel injection valve for injecting fuel from each nozzle hole has been known, in which a thin nozzle hole plate formed a plurality of nozzle holes is disposed in fuel downstream side of a valve portion formed of a valve member and a valve seat. In such a fuel injection valve, the nozzle hole generally has the same diameter from a nozzle hole inlet to a nozzle hole outlet. When fuel flows into such a nozzle hole with the same diameter, the fuel does not spread along an inner circumferential surface of the nozzle hole and is injected in a liquid column shape. The fuel formed in such a liquid column shape is resistant to atomization and combustion in an internal combustion is deteriorated.
On the contrary, there is a fuel injection valve, for example, disclosed in JP-A-2001-317431. FIG. 7 is a sectional view of a nozzle hole plate 21 thereof. The following fact has been known. As shown in FIG. 7, a nozzle hole axis line (chain double dashed line) is inclined with respect to a nozzle hole plate center line (dashed line). Furthermore, a nozzle hole outlet 22 is enlarged outwardly with respect to the nozzle hole plate center line so that the nozzle hole outlet 22 has larger diameter than a nozzle hole inlet 23. That is, a nozzle hole having a taper shape is inclined with respect to the nozzle hole plate center line. Whereby fuel injected from a nozzle hole 24 is prevented from becoming a liquid column so that the fuel spreads to become a liquid film and tends to be atomized.
[Patent Reference 1]
JP-A-2001-317431 (FIG. 7)
However, when the taper-shaped nozzle hole as described above is formed in the nozzle hole plate, very complicated process is required for its manufacture and size control, so that there are problems that deterioration of productivity of the fuel injection valve and an increase in cost are caused. Also, it has been generally known that atomization of fuel becomes better as a thickness of the nozzle hole plate is thinner. However, when the thickness of the nozzle hole plate is thinned, a spray angle of the fuel injected from the nozzle hole becomes large. Therefore, it is difficult that the nozzle hole plate has a certain extent of plate thickness, for example, 0.1 mm or less for reason of aspects of directivity of fuel spray and strength of the plate. Thus, it is inevitable to sacrifice the atomization of fuel to a certain extent.